Hello,
From what I can tell, this feature is still being worked on by R&D...at present, you can sign VIs for the LabVIEW player with the "Sign VIs" menu option. In the future we will have the ability with that "Validate VIs" option to check LLBs and subdirectories to find out which VIs are signed and which are not.
I hope this sheds some light on the issue for you. Please let me know if you have any other questions, and have a nice day.
Sincerely,
Darren N.
NI Applications Engineer